It seems that astronomers have found the closest known black hole to Earth, a strange little object called the “Unicorn” that hides only 1,500 light-years from us.
The nickname has a double meaning. The candidate for the black hole not only lives in the constellation Monoceros (the “unicorn”), the incredibly small mass – about three times larger than that of sun – makes it almost unique.
Because the system is so unique and so strange, you know, it certainly justified the nickname “Unicorn,” the leader of the discovery team Tharindu Jayasinghe, a doctor of astronomy. Ohio State University student said in a new video clip school made to explain the discovery.
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The “unicorn” has a companion – a swollen one giant red star which is nearing the end of its life. (Our sun will swell like a red giant in about five billion years.) This companion has been observed by a variety of instruments over the years, including the All Sky Automated Survey and the Transiting Exoplanet Survey Satellite.
Jayasinghe and his colleagues analyzed that large set of data and noticed something interesting: the light of the red giant periodically changes in intensity, suggesting that another object pulls the star and changes its shape.
The team determined that the object being fired is probably a black hole – one housing only three solar masses, based on details about the star’s speed and light distortion. (For perspective: the supermassive black hole in the heart of our Milky Way galaxy contains about 4.3 million solar masses.)
“Just as the moon’s gravity distorts the Earth’s oceans, causing the sea to swell to and from the moon, producing high tides, so the black hole distorts the star in a football-like shape, with one axis longer than the other.” co-author of the study Todd Thompson, president of the Ohio State Department of Astronomy, he said in a statement. “The simplest explanation is that it’s a black hole – and in this case, the simplest explanation is the most likely.”
This explanation, though it probably is, is not set in stone; The “unicorn” remains a candidate for the black hole at this time.
Very few such super-light black holes are known because they are incredibly hard to find. Black holes crowd everything, including light, so astronomers have traditionally detected them by observing the impact they have on the environment (although we recently obtained the first direct image of a black hole, thanks to the Horizon Event Telescope). And the smaller the black hole, the smaller the impact.
But efforts to find extremely low-mass black holes have increased significantly in recent years, Thompson said, so we could soon learn much more about these mysterious objects.
“I think the field is heading towards this, to really identify how many small masses, how many intermediate masses and how many black holes with large masses, because every time you find one it gives you an idea of what stars the collapse, which explodes and which are between them, “he said in a statement.
Jayasinghe and his team report the detection of the “Unicorn” in a paper that was accepted for publication in the Monthly Notices of the Royal Astronomical Society. You can read it for free on the online prepress website arXiv.org.
Mike Wall is the author of “There“(Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for extraterrestrial life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.